It is well known to persons skilled in the art of oil recovery that the amount and rate of oil production from many reservoirs can be increased by introducing carbon dioxide into the reservoir. Carbon dioxide is readily absorbed by the formation petroleum, which results in two benefits; namely, the oil volume is increased as carbon dioxide is absorbed, and the viscosity of the oil or petroleum is decreased. Both of these phenomenon lead to increased oil recovery. Enhanced oil recovery methods employing carbon dioxide injection have been used successfully in many fields, and generally the oil recovery methods employing carbon dioxide may be categorized as either a carbon dioxide drive process or a push-pull carbon dioxide stimulation process. In the drive process, a quantity of carbon dioxide is injected into a reservoir and then displaced by a less expensive drive fluid such as water or natural gas, which accomplishes displacement of petroleum through the formation to another, remotely located production well from which it is recovered to the surface of the earth. In the second type of enhanced oil recovery process, carbon dioxide is injected into a reservoir by a well in fluid communication therewith, and allowed to soak for a predetermined period of time, after which the oil having carbon dioxide dissolved therein, is back flowed into the same well as was utilized for carbon dioxide injection and thereby recovered to the surface of the earth. This latter technique is sometimes referred to as push-pull or huff-and-puff carbon dioxide flooding. While the first method described, the multi-well carbon dioxide flooding drive procedure recovers relatively large quantities of petroleum, the improved recovery usually requires that miscibility be obtained in the reservoir, which requires high injection pressures and frequently necessitates the addition of hydrocarbon solvents to achieve a true miscible displacement condition. Also, a significant quantity of carbon dioxide is injected and long time periods are required between injection of carbon dioxide before the increased oil recovery is obtained. By contrast, carbon dioxide stimulation by the push-pull method requires much less carbon dioxide and the stimulated increase in oil production is achieved in a much shorter time frame, in the order of weeks rather than years. Of course, a large field may be exploited by the push-pull carbon dioxide stimulation technique by simultaneous or sequential use of plurality of wells, each being utilized as an injection well in the first step of the stimulation process and as a production well in the second step. The term "single well" push-pull carbon dioxide stimulation as is sometimes applied to this process only means that the same well is used for both injection and production, and the process can be applied with only a single well.
While the carbon dioxide push-pull stimulation technique is frequently commercially successful, the results in some fields are sometimes less successful than had been predicted, because the production flow rate of petroleum from the formation into the well after injection of carbon dioxide and soak is much lower than it was expected. The reason for the less-than-expected production flow rate has never been satisfactorily explained, and no subsequent treatment is known which will improve the flow rate. Accordingly, despite the fact that push-pull carbon dioxide stimulation has been effective in some applications, there is still a significant unfulfilled commercial need for a method which will permit achievement of the anticipated benefit from push-pull carbon dioxide stimulation process with improved production rates from the wells used in the process.